This invention relates to smoking articles in which tobacco flavor media are heated to release tobacco flavors. More particularly, this invention relates to electrically heated smoking articles.
An electrically heated smoking article is described in commonly-assigned U.S. Pat. No. 5,060,671, which is hereby incorporated by reference in its entirety. That patent describes an electrically heated smoking article which is provided with a disposable set of electrical heating elements on each of which is deposited an individual charge of tobacco flavor medium containing, for example, tobacco or tobacco-derived material. The disposable heater/flavor unit is mated to a more or less permanent unit containing a source of electrical energy such as a battery or capacitor, as well as control circuitry to actuate the heating elements in response to a puff by a smoker on the article or the depression of a manual switch. The circuitry is designed so that at least one but less than all of the heating elements are actuated for any one puff, so that a predetermined number of puffs, each containing a pre-measured amount of tobacco flavor substance, is delivered to the smoker. The circuitry also preferably prevents the actuation of any particular heater more than once, to prevent overheating of the tobacco flavor medium thereon and consequent production of undesired compounds yielding off tastes.
In such a smoking article, the heating elements are disposed of along with the spent tobacco flavor medium. This results in increased costs to the smoker, who must buy new heating elements with each refill of tobacco flavor medium. The volume of material disposed of is also greater when the heating elements must be disposed of.
In addition, when the heating elements are disposable, they must by their nature be removable. As a result, there is sometimes excessive contact resistance at the connection where the removable heaters are electrically connected to the source of electrical energy, resulting in increased power consumption. Furthermore, that connection must be designed to withstand repeated insertion of new heating elements after each use.
Also, when the heating elements are disposable, the heater electrical resistance may vary from heater to heater, resulting in variations in power consumption which, in turn, can lead to variations in temperature. As it is the temperature to which the tobacco flavor medium is heated that determines the characteristics of the tobacco flavor substance, those characteristics will also vary.
The above-discussed disadvantages associated with U.S. Pat. No. 5,060,671 are addressed by copending, commonly-assigned U.S. patent application Ser. No. 07/666,926, filed Mar. 11, 1991, now abandoned in favor of filewrapper continuation application Ser. No. 08/012,799 filed Feb. 2, 1993, which is hereby incorporated by reference in its entirety. That application describes an electrically heated smoking article that has reusable heating elements and a disposable portion for tobacco flavor generation. The disposable portion preferably includes a flavor segment and a filter segment, attached by a plug wrap or other fastening means.
A disadvantage of reusable heating elements is that residual aerosol can settle and condense on the heating elements and other permanent structural components of the smoking article, resulting in the generation of undesirable aerosol components if the residual aerosol is reheated after new disposable tobacco flavor medium is inserted into the article. Such residue is referred to as "fixture contamination."
The disadvantages associated with condensed residual aerosol are addressed by copending, commonly-assigned U.S. patent application Ser. No. 07/943,504 (PM-1550), filed concurrently herewith, which is hereby incorporated by reference in its entirety. That application describes an electrical smoking article having a permanent heater fixture and a removable tobacco flavor unit for delivering to a consumer a tobacco flavor substance. The heater fixture and tobacco flavor unit are designed and arranged to prevent condensation of aerosol on certain components, so that the generation of undesirable aerosol components is minimized.
Whether a smoking article employs disposable or permanent electrical heaters, it is desirable that the heaters are able to reach an operating temperature of between about 200.degree. C. and about 700.degree. C. when in thermal contact with tobacco flavor medium with minimum electrical energy input. Such operating temperatures are effective in efficiently generating tobacco flavor substances.
It is also desirable that the smoking article minimize the generation of undesirable flavors and the heating of non-tobacco flavor material.
It is further desirable that the tobacco flavor material of the smoking article generates large quantities of aerosol and flavorants with minimum electrical energy input.